Transmissions are used in vehicles to transfer torque from a drive unit to a vehicle load. For example, many transmissions transfer the torque from a vehicle engine to a vehicle load produced at the interface of the vehicle's wheels when a vehicle is being driven along a road. Typical transmissions include a gear train that is reconfigurable among a number of gear ratios to establish a particular rotational drive ratio between the vehicle engine and the vehicle load. A transmission system can include additional features such as a retarder to affect overall performance. A retarder, for example, can be any device used to assist or replace a primary braking system on a vehicle.
At colder temperatures, fluid internal to the transmission and retarder can have a greater viscosity. In some transmission systems, fluid can be trapped or accumulated in different portions of the system. In these instances, there is generally less fluid in a reservoir or sump of the transmission system readily available to apply clutches and the retarder as desired. This can be particularly problematic at colder temperatures when the fluid viscosity is high and there is less fluid available to pump throughout the system.